Interferon inducers activate macrophages and inhibit the growth of certain animal tumors. While there is no proof that interferon is involved in these effects, exogenous interferon, administered in rather high doses has also been shown to inhibit tumor growth. We propose to: 1) Examine the production of interferon by cultures of normal or activated mouse macrophages. Macrophages will be obtained from animals pre-treated with interferon inducers or the macrophages will be incubated in vitro with the inducers. 2) Investigate the cellular mechanisms involved in the production and release of interferon by macrophages. Specifically, to determine whether interferon can be released from macrophages by agents that induce exocytosis, and to investigate the possible storage of exogenous interferon by macrophages. 3) Determine whether interferon-rich preparations can activate macrophages as measured by the ingestion of IgG or complement-coated erythrocytes or by the enhancement of macrophage cytotoxicity to target cells in an allogeneic system.